Due to good dynamic properties and comparatively compact structure, piezo-electric actuators are being more frequently utilized as drives in modern gasoline and diesel injection systems. Currently under development, in particular, are what are referred to as directly driven valve systems wherein the piezo-electric actuator acts directly without interposition of a stroke transformer or indirectly on a valve needle or a valve lifter, whereby the needle or, respectively, lifter stroke thus approximately corresponds to the adjustment path generated by the actuator. Independently of the respective operating temperature of the motor, the valve systems must meet the strictest demands with respect to the dosing precision and the reproducibility of the injected fuel quantity. An injection valve that is fully functional and works with a high electro-mechanically efficiency in the temperature range=-40.degree. C. to 140.degree. C. therefore requires elements for the compensation of thermally conditioned length changes of the piezo-electric actuator, of the other mechanical components (valve lifter, valve needle, etc.) and of the housing.
Great Britain reference 2,228,769 A, U.S. Pat. No. 4,995,587 and European reference 0,218,895 B1 disclose injection, dosing or control valves directly driven or equipped with a stroke transformer.
For the compensation of temperature-conditioned length changes of the piezo-electric actuator, Great Britain reference 2,228,769 A proposes that a metal cylinder of a suitable length be arranged between the actuator and the valve lifter.
The element compensating temperature-conditioned length changes of the injection valve disclosed by U.S. Pat. No. 4,995,587 is essentially composed of a pot-shaped part that is screwed to the valve housing and closed at the actuator side and of a piston displaceably arranged in the pot-shaped part. The spring-loaded piston is screwed to a supporting plate lying against the actuator and face. An elastomer serves as a filler for the compensation chamber formed by the piston and the pot-shaped part.
The piezo-electric actuator of the injection valve disclosed by European reference 0,218,895 B1 is supported on a damping piston guided play-matched in a housing bore. The damping piston and the housing bore form a fluid-filled chamber that is in communication with a compensation volume via an annular gap present between the damping piston and the housing bore.
In the known valves, the bearing of the piezo-electric actuator has not been satisfactorily resolved, this having a disadvantage effect on the electro-mechanical efficiency of the drives. Moreover, the stiffness of the respective bearings which is highly reduced due to the compensation elements forces an employment of over-long piezo-electric actuators in order to compensate for the losses of actuating path and actuating force produced by expansion of the mechanical components.